1. Field of the Invention
The present invention relates to Radio Frequency (RF) tags and, more particularly, to three dimensional RF tag signatures.
2. Description of the Related Art
Radio Frequency tags, also known as Radio Frequency Identification (RFID) tags use electromagnetic radiation to temporarily charge a circuit, which may be programmed to wirelessly transmit a data code. If the data transmitted by the circuit is received by an RF tag reader, it is possible to determine that the RF tag is in the proximity of the RF tag reader. By causing different chips to transmit different RF tag codes, the identity of the RF tag may be determined, which will allow a RF tag processing system interfaced with the RF tag reader to uniquely place that RF tag in a particular place at a particular point in time. Thus, by associating the RF tags with individual articles that are to be tracked, it is possible to keep track of many different articles electronically. RF tags may be used in many applications, and the number of applications of RF tags has been increasing dramatically in the last few years. For example, RF tags are used in retail establishments to keep track of merchandise, in manufacturing to keep track of inventory, in corporations for example in building access badges, and in many other fields.
FIG. 1 shows an example RF tag. As shown in FIG. 1, a standard RF tag 10 includes a coil 12 that will be used to capture electromagnetic radiation to produce a current. As is well known, changing an electromagnetic field relative to a coil will cause an electrical current to flow in the coil. Thus, by modulating an electromagnetic field it is possible to cause a current to be generated in the coil of an RF tag. Where the coil 12 is connected to an electromagnetic circuit 14, and the electrical current is used to power to circuit 14. The circuit may be used for many different things, but generally is configured to transmit a tag response including a tag code that may be read by a RF tag reader 20 (see FIG. 2). RF tags are well known, and many different types and sizes/shapes of RF tags and circuits have been developed.
As shown in FIG. 2, in operation a RF tag reader 20 generates a strong electromagnetic field 22 which will cause a current to be generated in any RF tags within a given distance of the RF tag reader. When an RF tag 10 comes into proximity of the RF tag reader 20, the RF tag will generate the tag response 24 which may be sensed by the reader 20 if the tag is sufficiently close to the reader 20.
RF tags provide an indication of presence of the tag relative to the reader, but generally do not provide an indication of where the RF tag is located within the reader's field of view. While it is possible to use an RF tag reader that has one or more directional antennas to help determine the relative position of the RF tag, doing so reduces the ability of the RF tag reader to detect the presence of RF tags outside of the directional antenna beam.
Similarly, when an RF tag is associated with an article, for example where RF tags are to be used to track boxes of merchandise or luggage, sensing the presence of an RF tag will enable the reader to determine the rough location of a particular article at that particular point in time. The RF reader is not able however, to determine the state of the article or whether the article has been damaged or altered since the last time the RF tag presence was sensed. Accordingly, while RF tags are very useful for tracking where articles are at particular points in time, it would be advantageous to provide a way in which the RF tags could provide additional information about the articles being tracked.